1. Field of the Invention
The present invention relates to a method for polishing a surface of a workpiece, by means of a tool rotating about a tool axis, whereby the workpiece is contacted in at least one region of the workpiece surface by a respective momentarily contacting surface that is a subarea of a surface for machining, which for its part is at least part of a polishing surface of the tool, whereby the tool axis intersects the polishing surface.
2. Description of the Background Art
Below, the term surface for machining may denote the entirety of all surfaces of a rotating tool touching the workpiece during a revolution of the tool. The momentarily contacting surface may be referred to as the surface that is in contact with the workpiece at a respective point in time.
In the conventional art according to FIG. 1, a rotating tool 2 is moved on a likewise rotating workpiece 1, whereby the rotating tool 2 is composed of a rubber membrane or a pestle with a glued-on polyurethane membrane, e.g., a polishing foil or polishing surface 2.1. The tool rotates about a tool axis 2.2, the workpiece rotates about a workpiece axis 1.2. The polishing foil exhibits a curvature and rests with it's rotational center and a circular machining area 2.4 around the rotational center on the workpiece 1 during the machining. Thereby the polishing foil is being pressed on, e.g. by compressed air or a deforming elastomer. Removal at the workpiece is achieved by the polishing foil as well as by a permanently fed liquid. The membrane or the pestle is always placed perpendicularly onto the workpiece surface 1.1 and slowly guided on a radius over the workpiece 1 by means of a CNC program. The sub figures a), b) and c) show discrete points in time of such a motion in a lateral view as well as in a top view, respectively. The removal is controlled by choosing the speed profile on the radius in order to achieve the desired shape of the workpiece 1.
This method, however, only yields a small amount of removal. Moreover, the polishing tool is worn out comparatively fast. Furthermore for polishing the border area the tool has to protrude at least partially over the workpiece as depicted in FIG. 1c). In doing so the tool can be very strongly worn out and destroyed by the lenses outer edge, especially at high air pressure. This method is suitable for convex or concave rotationally symmetric workpieces only, but not for free-form surfaces or non-rotating workpieces.
In another method, depicted in FIG. 2 a wheel-shaped polishing tool 2 rotating about a tool axis 2.2 is guided over a workpiece surface 2.1 of a workpiece 1 rotating about a workpiece axis 1.2. The polishing surface 2.1 is mounted on the contact surface of the wheel-shaped polishing tool 2, in this case. The entire polishing surface 2.1 acts as a machining surface 2.4 whereby only one momentarily contacting surface 2.3 is in contact with the workpiece surface 1.1 at every point in time. However there is a risk for polishing a hole in the center of the workpiece because of the small area machined there.
The machining precision of both methods, however, is limited.